#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <vector>
using namespace std;

int main()
{
    int w = 0, h = 0;
    int count = 0;
    cin >> w >> h;

    vector<vector<int>> a;
    a.resize(w);
    for (int i = 0; i < w; i++)
    {
        a[i].resize(h, 1);
    }

    for (int i = 0; i < w; i++)
    {
        for (int j = 0; j < h; j++)
        {
            if (a[i][j] == 1)
            {
                count++;
                if (i + 2 < w)
                {
                    a[i + 2][j] = 0;
                }
                if (j + 2 < h)
                {
                    a[i][j + 2] = 0;
                }
            }
        }
    }

    cout << count;
    return 0;
}